The present invention generally relates to motors and, more particularly, to a reinforced motor for reducing the amplitude of operational vibrations.
Vibrations can develop on motors, such as the Form W electric motor manufactured and sold by General Electric Company, at a variety of different frequency levels for any number of different reasons. If the amplitude of the vibrations is higher than an acceptable threshold value prescribed by a manufacturer and/or a customer, the motor will not pass a quality inspection at the manufacturer site and/or the customer site. Also, a motor which has passed a quality inspection may develop vibration problems in the field after assembly into an electric appliance or because of small changes in the structure of the motor assembly developed during operational service as part of an appliance. A high amplitude vibration of the motor is undesirable, as it creates vibration and noise problems on the appliance powered by the motor.
With respect to the Form W motor, vibrations at frequencies which are multiples of twice line frequency, 120 Hz, and in particular 360 Hz and 480 Hz, are a result of asymmetric electromagnetic forces developed between the stator and rotor of the motor. Vibrations at the 360-480 Hz frequency level occur as a direct result of excitation electromagnetic forces at the same frequency level. The excitation electromagnetic forces are internal forces for the Form W motor. The structural components of the Form W motor that join the stator and rotor are called end shields. Each Form W motor has upper and lower end shields attached at opposite ends of the stator. The end shields rotatably support the rotor centrally of the stator. The end shields are compliant components made of lightweight sheet metal which can deform due to asymmetric electromagnetic forces, thereby allowing vibrations of high amplitude at the 360-480 Hz frequency level. The most compliant end shield of the two end shields of the Form W motor is the one end shield with a switch opening, referred to as the open end shield. Experiments and Finite Element Analysis of end shields have shown that the open end shield deforms when vibrating at 360 Hz on the Form W motor. The open end shield, particularly, develops high levels of bending deformation above the switch opening when loaded radially in a direction parallel to the plane of the side wall of the enclosure with the switch opening.
Consequently, a need exists for a structural modification of the motor that will reduce or substantially eliminate the aforementioned vibration and noise problems generated by the motor without introducing any new problems in place thereof.